IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Monday Sessions
       Session SC-MoM

Paper SC-MoM6
Nanoscale Phase Formation at Cu(In,Ga)Se@sub 2@ Surfaces

Monday, October 29, 2001, 11:20 am, Room 124

Session: Band-Engineered Electronic Materials
Presenter: Y.M. Strzhemechny, The Ohio State University
Authors: Y.M. Strzhemechny, The Ohio State University
G.H. Jessen, The Ohio State University
J.I. Choi, The Ohio State University
L.J. Brillson, The Ohio State University
D.-X. Liao, University of Illinois at Urbana-Champaign
A. Rockett, University of Illinois at Urbana-Champaign
Correspondent: Click to Email
Copper indium gallium diselenide (CIGS) exhibits unique optical properties that make it well suited for thin film devices as a polycrystalline material. The engineered electronic properties of CIGS heterojunctions depend sensitively on the CIGS near-surface region. The nanoscale electronic structure and chemistry of this layer and, specifically, point defect segregation and surface phases are thought to be critical to such device structures, yet they are relatively unexplored. We employed low-energy depth-resolved cathodoluminescence (CL) and Auger Electron Spectroscopy (AES) to measure the local band and defect properties as well as composition variations of CIGS films grown epitaxially with (001), (110), and (112) orientations on GaAs wafer substrates. CL spectra reveal near band edge (NBE) emissions of 1.10 to 1.15 eV, depending on growth and orientation as well as the presence of a deep-level transition with energy 0.89-0.93 eV confined to within a few hundred nm of the free CIGS surface. The NBE energies vs. AES compositions agree with the reported variation in band gap vs. Cu/(In+Ga) ratio. The deep defect-associated feature relative to the higher lying peak has maximum intensity at the surface and decreases exponentially into the bulk with a decay length of ca. 50 nm. Auger depth profiles for (110) and (001) orientations show 16% and 20%, respectively, depletion in Cu content within tens of nanometers of the surface. Deep level and NBE energies exhibit a strong dependence on surface Cu and Ga content. Both increase by tens of meV away from the free surface, in line with the increased band gap and changes in composition. The Cu-deficient surface layers are consistent with an ordered vacancy compound proposed for the CIGS surface. The observed gap and composition changes confirm the existence of a nanoscale surface phase whose properties can impact charge generation and recombination for solar energy-generating structures.